Fancy Dress Ideas for World Book Day

Each year my daughters school encourage all pupils & teachers to dress as a character from a book for World Book Day and it is such a hassle! She's in year three and when she was younger it was easy they all just went in a Disney Princess dress. Now she;s older, wants to look cool, thinks she;s a bit old for fancy dress but still wants to take part as otherwise she'll stand out (!). Any ideas? I can be slightly creative, but not very, but its the ideas that i lack!
Thanks